Polymer alloys comprising two resins are classified into incompatible polymer alloys, compatible polymer alloys, and partially compatible polymer alloys. For compatible polymer alloys, two resins are compatible in the whole practical region at a temperature from glass transition temperature to decomposition temperature. For incompatible polymer alloys, two resins are incompatible in the whole region. For partially compatible polymer alloys, two resins are compatible in some regions and phase-separated in other regions, resulting in spinodal decomposition. In a compatible polymer alloy, resins are generally compatible at the molecular level, and, consequently, intermediate properties between the mixed resin components are often obtained. Thus, to make the most of the properties of two resins, studies on incompatible and partially compatible polymer alloys are actively conducted.
JP 2003-286414 A discloses making polycarbonate and polybutylene terephthalate have a two-phase continuous structure with a structure cycle of 0.001 to 1 μm or a dispersed structure with an interparticle distance of 0.001 to 1 μm by spinodal decomposition, thereby improving the mechanical strength. In the method described in JP '414, polycarbonate and polybutylene terephthalate are compatibilized by applying shear stress in an extruder, and then spinodal decomposition is caused to form an alloy structure.
WO 2009/041335 discloses that a polymer alloy having a finely and uniformly controlled structure can be obtained such that oligomers or monomers are used as precursors of at least one thermoplastic resin component among the thermoplastic resin components constituting the polymer alloy, thereby compatibilizing the thermoplastic resin component with other thermoplastic resin components and, further, chemical reaction is caused in the co-presence of two resins to induce spinodal decomposition.
Incompatible polymer alloys generally have a spherically dispersed structure with a dispersion size of 1 μm or more and, in recent years, attempts have been made to reduce the dispersion size.
JP 2009-46641 A discloses the toughness of an incompatible polymer alloy comprising polyetherimide and polyphenylene sulfide is improved by increasing the shear force during melt-kneading and adding a compatibilizer to achieve dispersion with a number average dispersed particle size of 1000 nm or less.
JP 2011-46936 A and WO 2011/013517 disclose that a polymer alloy having a finely and uniformly controlled structure can be obtained by melt-kneading by chaotic mixing, which is achieved by using a screw effective to create a chaotically mixed state and, further, by setting the temperature in a kneading zone at a temperature 1 to 70° C. higher than the glass transition temperature of a resin having a highest glass transition temperature among the resins used.
The method described in JP '414 has the limitation that when using a combination of common incompatible resins, a two-phase continuous structure with a structure cycle of 0.001 to 1 μm or a dispersed structure with an interparticle distance of 0.001 to 1 μm cannot be formed and, further, had a problem in that it is difficult to uniformly apply shear stress, which results in poor uniformity of a dispersed phase.
Also in the method described in WO '335, it is necessary to compatibilize precursors of at least one thermoplastic resin component with other thermoplastic resin components. Thus, there is a limitation that when using a combination of incompatible resins, a two-phase continuous structure with a structure cycle of 0.001 to 1 μm or a dispersed structure with an interparticle distance of 0.001 to 1 μm cannot be formed.
The method of JP '641 provides a structure with ununiform spherical dispersion, and the improving-effect on heat resistance was not sufficient.
The method of JP '936 and WO '517 is a kneading method using at least one amorphous resin. While in the case of a polymer alloy of a combination of crystalline resins, which have a low glass transition temperature, there is the problem in that when melt-kneading is performed setting the temperature of a kneading zone at a temperature 1 to 70° C. higher than the glass transition temperature, the polymers are crystallized during the melt-kneading under the influence of crystallization and could not be discharged. When melt-kneading two or more crystalline resins, the melt-kneading is generally performed at or higher than the melting point of a resin having a highest melting point among the crystalline resins used. However, since the viscosity of crystalline resins is sharply reduced at or higher than their melting points, a chaotically mixed state is not created because of the too low melt viscosity, resulting in a structure with ununiform dispersion, and the improving effect on heat resistance, wet-heat resistance, and mechanical properties is not sufficient. Further, using an amorphous resin results in poor durability and chemical resistance compared to when using a polymer alloy of a combination of crystalline resins and, therefore, it is problematic to use an amorphous resin as a structural material that requires durability.
It could therefore be helpful to provide a polymer alloy of a combination of crystalline resins with excellent heat resistance, wet-heat resistance, and mechanical properties.